Pulley pressure control apparatus for belt-driven continuously variable transmission

Abstract

A road surface friction coefficient calculator is to detect a coefficient of friction on a road surface. A braking force calculator is to detect the braking force of a vehicle. A decelerating calculator is to determine whether the vehicle transitions to a decelerating travel mode. The pulley pressure controller is to control pulley pressure in a belt-driven continuously variable transmission. The pulley pressure controller is to increase the pulley pressure by an additional amount when the decelerating calculator determines the vehicle transitions to the decelerating travel mode while the coefficient of friction detected by the road surface friction coefficient calculator is equal to or lower than a reference value. The pulley pressure controller is to reduce the additional amount when the braking force calculator detects an increase in the braking force in the decelerating travel mode.

What is claimed is: 
     
       1. A pulley pressure control apparatus for a belt-driven continuously variable transmission that includes a drive pulley connected to a power source, a driven pulley connected to a driving wheel, and an endless belt looped over the drive pulley and the driven pulley, and that transmits drive power of the power source to the driving wheel while changing a gear ratio, the pulley pressure control apparatus comprising:
 a pulley pressure controller that controls pulley pressure in the belt-driven continuously variable transmission; 
 a road surface friction coefficient calculator that detects a coefficient of friction on a road surface; and 
 a braking force calculator that detects a braking force of a vehicle, wherein 
 when the vehicle transitions to a decelerating travel mode with the road surface friction coefficient calculator detecting that the coefficient of friction on the road surface is a predetermined value or lower, the pulley pressure controller increases the pulley pressure by a predetermined additional amount, and 
 when the braking force calculator detects an increase in the braking force in the decelerating travel mode, the pulley pressure controller reduces the additional amount for the pulley pressure. 
 
     
     
       2. The pulley pressure control apparatus for the belt-driven continuously variable transmission according to  claim 1 , wherein
 the pulley pressure controller reduces the additional amount for the pulley pressure more when an amount of the increase in the braking force detected by the braking force calculator is larger. 
 
     
     
       3. The pulley pressure control apparatus for the belt-driven continuously variable transmission according to  claim 1 , wherein
 when the braking force detected by the braking force calculator becomes zero, the pulley pressure controller reduces the additional amount for the pulley pressure to zero. 
 
     
     
       4. A pulley pressure control apparatus for a belt-driven continuously variable transmission, the pulley pressure control apparatus comprising:
 a road surface friction coefficient calculator to detect a coefficient of friction on a road surface; 
 a braking force calculator to detect the braking force of a vehicle; 
 a decelerating calculator to determine whether the vehicle transitions to a decelerating travel mode; 
 a pulley pressure controller to control pulley pressure in the belt-driven continuously variable transmission that includes a drive pulley connected to a power source, a driven pulley connected to a driving wheel, and an endless belt looped over the drive pulley and the driven pulley, and that is configured to transmit drive power of the power source to the driving wheel while changing a gear ratio; and 
 the pulley pressure controller to increase the pulley pressure by an additional amount when the decelerating calculator determines the vehicle transitions to the decelerating travel mode while the coefficient of friction detected by the road surface friction coefficient calculator is equal to or lower than a reference value, the pulley pressure controller being to reduce the additional amount when the braking force calculator detects an increase in the braking force in the decelerating travel mode. 
 
     
     
       5. The pulley pressure control apparatus according to  claim 4 , wherein
 the more increase the braking force calculator detects, the more additional amount the pulley pressure controller reduces. 
 
     
     
       6. The pulley pressure control apparatus according to  claim 4 , wherein
 when the braking force detected by the braking force calculator becomes zero, the pulley pressure controller reduces the additional amount to zero.